1 files changed, 47 insertions, 0 deletions
diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
index 7d6ffc9f3..3e4899efc 100644
--- a/src/libexpr/attr-set.hh
+++ b/src/libexpr/attr-set.hh
@@ -113,5 +113,52 @@ public:
     friend class EvalState;
 };
 
+/* A wrapper around Bindings that ensures that its always in sorted
+   order at the end. The only way to consume a BindingsBuilder is to
+   call finish(), which sorts the bindings. */
+class BindingsBuilder
+{
+    Bindings * bindings;
+
+public:
+    // needed by std::back_inserter
+    using value_type = Attr;
+
+    EvalState & state;
+
+    BindingsBuilder(EvalState & state, Bindings * bindings)
+        : bindings(bindings), state(state)
+    { }
+
+    void insert(Symbol name, Value * value, ptr<Pos> pos = ptr(&noPos))
+    {
+        insert(Attr(name, value, pos));
+    }
+
+    void insert(const Attr & attr)
+    {
+        push_back(attr);
+    }
+
+    void push_back(const Attr & attr)
+    {
+        bindings->push_back(attr);
+    }
+
+    Value & alloc(const Symbol & name, ptr<Pos> pos = ptr(&noPos));
+
+    Value & alloc(std::string_view name, ptr<Pos> pos = ptr(&noPos));
+
+    Bindings * finish()
+    {
+        bindings->sort();
+        return bindings;
+    }
+
+    Bindings * alreadySorted()
+    {
+        return bindings;
+    }
+};
 
 }